The present invention relates to a transmission internally meshing a planetary gear structure used as a reducer for controlling an automated and precision control machine such as a numerical controlled apparatus.
In general, automated and precision control machines equipped with reduction gears to reduce high rotary speed conveyed through a motive axis of power source such as an electric-powered motor or a servomotor. The reducer gears are required to move precisely and to be miniaturized, in order to reduce a size of an automated and a precision control machines and to increase precision of automated and precision control machines.
One of the conventional reducers is an RV series of Vigo Drive(trademark) developed and marketed by Teijin Seiki. The RV series of Teijin Seiki has been endowed with a plurality of pinch differences and a plurality of first-step reduction gears at an output end for securing an insertion space for a motive axis of power source inside an input shaft, thus conveying deceleration movement.
The RV series of Teijin Seiki, however, have the following problems:
(1) Since a plurality of pinch differences is used, a deceleration ration is frequently calculated as non-terminating decimals when calculating the deceleration ratio. Therefore, errors are accumulated when the reducer is frequently used and it leads to a decrease in the precision of deceleration movement.
(2) The RV series of Teijin Seiki can be comfortably applied to high-reduction gear ratio, as the diameter of an output end of the input shaft is made small in order to place a first-step reduction gear at the output end. However, extra parts are required when it is applied to low-reduction gear ratio, thus making the reducer bigger.
(3) Since first-stage reduction gears are located at an output end, extra parts for oil-sealing are required in order to prevent oil leakage such as grease from the circumferential portion of the first-step reduction gears. Therefore, the manufacturing cost and weight are increased.
(4) Since a first-step reduction gear is located at an output end, the length of an insertion space in an input shaft is ensured for the insertion of a motive axis of power source. However, the caliber of the insertion space is limited exceedingly due to the use of pinch differences.
(5) When installing a first-step reduction gear at an input end to address the above problems, the diameter of the insertion space for the motive axis insertion of power source gets very small due to the first-step reduction gear in a body with a prescribed diameter and the deceleration range gets limited exceedingly.
(6) Because pinch differences are adopted, the number of pins accommodated in a predetermined body gets limited due to the diameter of a pinxe2x80x94about 2 mm, thus making the deceleration range limited exceedingly.
Another reducer with an internal planetary gear is described in detail in commonly owned Korean Patent No. 242207, which is incorporated herein by reference as if fully set forth herein. The reducer comprises a main crank structure that is combined with a motive axis of power source in an Oldham coupling method. The reducer receives the conveyed rotary power from the power source, a plurality of planetary gears. The plurality of planetary gears conducts deceleration movement translating and rotating according to the rotation of supplementary crank structures and a plurality of supplementary crank structures that execute translation and rotation movement engaged with the planetary gears.
The reducer of the Korean Patent No. 242207, however, has cases where the rotary movement of the main crank structure and the supplementary axes are not perfectly aligned with each other. For example, the perfect alignment may not be achieved due to reasons of processing, assembling and deformation, as the supplementary crank structures are connected to the planetary gear that translate and rotate at the same time. In other words, the rotation of the supplementary crank structures is not regulated. Here, when the supplementary crank structures move, or when load is added from outside, a problem arises in that the supplementary crank structures vibrate periodically to the rotating direction, thereby dropping the qualities of precision and continuity of power transmission.
It is, therefore, an object of the present invention to provide a transmission internally meshing a planetary gear structure that can maintain the precision and continuity of power transmission reliably and also can be miniaturized. In this manner, problems of the conventional technologies mentioned above can be addressed.
It is another object of the present invention to provide a transmission internally meshing a planetary gear structure which is easy to oil-seal, and applicable to both high-reduction gear ratio and low-reduction gear ratio, thus making the reducer inexpensive and small.
A transmission internally meshing a planetary gear structure comprises: a body wherein an internal gear is formed on an outer circumferential surface; an input shaft wherein formed are serration on the outer circumferential surface and an insertion space inside for power source connection; a plurality of first planetary gears wherein formed are serrations that fit with those of the input shaft, thereby moving engaged with the input shaft; a plurality of crank structures which are equipped with both a number of coaxial lines having the identical axis and a number of eccentric components that is, located between the coaxial lines, having a predetermined eccentric amount but with phase differences to each other, and which rotate by the rotary movement of the first planetary gears; second planetary gears wherein the planetary gears are formed along the outer circumferential surface and engaged with the internal gears of the body, also formed is a central hole that the input shaft penetrates in the center and the eccentric components of the crank structures pass through a circumferential portion and conduct translation and rotation movement to the rotary movement of the crank structures; a precession prevention plate wherein a central hole penetrated by the input shaft is formed in the center, the coaxial lines at the back end of the crank structures penetrate the circumferential portion so that they are connected, and the generation of the precession is blocked when the crank structures rotate; and an output shaft plate wherein a central hole that the input shaft penetrates in the center, of which the circumferential portion is combined to the coaxial lines of the fore end of the crank structures and conveys the rotary power of the crank structures.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.